Streaming Hydro or "Run of River?"

Streaming Hydro systems are often referred to as Run of River
systems, because the river continues to run rather than being held
back by a dam as with Reservoir systems. Although we use the
term Streaming Hydro here, Run of River is still a
widely accepted term for this type of hydropower system.

"
Hydropower extracts energy from water as it flows by.

"Green hydropower continues to generate
electricity when the sun goes down and the wind stops blowing. "

Types of Hydropower, continued...

Streaming Hydropower: No Dam, No Lake

Streaming (Run of River) Hydroelectric Projects

In contrast to Reservoir designs,
Streaming Hydro projects use a completely different approach. First,
there is no dam or reservoir. Instead of a dam, Streaming Hydro
systems use a diversion to channel some of the water from a
stream into a pipe that supplies the water turbine. The rest of the
stream water continues past the diversion down its natural path.

Pictured is a Streaming Hydroelectric
powerhouse. A pipeline (not shown) extends from the powerhouse
up the hill to a diversion, and directs pressurized water to the
turbine inside the building. The water in the foreground has passed
through the turbine, and it rejoins the rest of the stream a few
feet away.

How Streaming Hydro Works

The diverted water flows down a pipeline
(known as a penstock), passing through a turbine to generate
electricity, and then recombining with the original stream. As we
discussed earlier, this pipeline is used to contain the water to
build high pressure at the bottom where it enters the turbine.

In effect, Streaming Hydro systems “borrow” a
portion of the stream’s water to produce power, returning it to the
stream after the energy is extracted. Unlike the Reservoir system,
Streaming Hydro does not change the natural course of the stream or
store water for future use.

This creates a couple of disadvantages. First,
without a reservoir there is no reserve capacity for peak load
periods. Second, because not all the water from the stream is being
used to generate electricity, the output of the hydroelectric system
is less than it could be with a Reservoir system.

Streaming Hydro Advantages

But Streaming Hydro has many advantages.
First, these systems help resolve the two major disadvantages of the
Reservoir system: fish migration and flooding. The stream still
flows in parallel with the hydro system, providing an unencumbered
path for fish migration. And since there is no reservoir, habitat
flooding is not an issue.

Another example of a Streaming Hydroelectric
powerhouse. Notice the pipeline feeding into the the rear of the
powerhouse.

Because most Streaming Hydro systems are
smaller – typically less than 30 megawatts – they occupy very little
space and tend to blend into the environment. This makes them ideal
for smaller streams and rivers where a Reservoir system wouldn’t be
appropriate. A side benefit is that transmission lines are much
shorter; in fact, they often reduce transmission losses by providing
locally generated power instead of requiring lines from large
generating plants that may be hundreds of miles away.

These are important considerations today, as
potential sites for large reservoir systems are extremely limited.
There are thousands of smaller streams that could be used for
Streaming Hydro with minimal visual and environmental impact.